Autonomous cooling of Kerr-cat qubits to minutes-long bit-flip times
Authors: Sergey Hazanov, Mikhail Svintsov, Uri Goldblatt, Barkay Guttel, Fabien Lafont, Serge Rosenblum
Abstract
Quantum error correction becomes more hardware efficient when physical noise is strongly biased towards one error channel. Cat qubits realize such a bias by encoding information in two opposite coherent states of a superconducting oscillator, so that bit flips are exponentially suppressed with photon number while phase-flip rates increase only linearly. In Kerr-cat qubits, a driven double-well potential confines these states and enables fast coherent control, but excitations can induce interwell switching, limiting bit-flip times to milliseconds. Here we show that the nonlinear interaction generating the confinement can also cool these excitations. When an intra-well transition becomes resonant with a lossy readout mode, excitations are transferred out of the qubit and dissipated, as established by spectroscopy and relaxation measurements. We observe the predicted exponential scaling of Kerr-cat bit-flip times with photon number, reaching 450 s, over five orders of magnitude beyond previous demonstrations. Phase-flip rates remain consistent with intrinsic photon loss at operating points with seconds-long bit-flip times. We further demonstrate fast Z gates without measurable degradation of bit-flip protection and single-shot readout with a bit-flip probability below $10^{-6}$ per measurement. Autonomous cooling thus brings minutes-long bit-flip protection to Kerr-cat qubits while retaining fast coherent control, without additional cooling drives or circuit elements.
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Enhancing Kerr-Cat Qubit Coherence with Controlled DissipationF. Adinolfi, D. Haxell, A. Bruno et al. · 2025 · cited 5 times · Not summarized yet
Enhancing Kerr-cat Qubit Coherence with Controlled Dissipation investigates dissipation-based coherence improvement in Kerr-cat qubits, while this paper cools excitations through a resonant lossy readout mode.
Abstract
Quantum computing crucially relies on maintaining quantum coherence for the duration of a calculation. Bosonic quantum error correction protects this coherence by encoding qubits into superpositions of noise-resilient oscillator states. In the case of the Kerr-cat qubit (KCQ), these states derive their stability from being the quasi-degenerate ground states of an engineered Hamiltonian in a driven nonlinear oscillator. KCQs are experimentally compatible with on-chip architectures and high-fidelity operations, making them promising candidates for a scalable bosonic quantum processor. However, their bit-flip time must increase further to fully leverage these advantages. Here, we present direct…
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Engineered two-photon dissipative confinement of a Kerr-cat qubit using SISIS quantum circuit refrigeratorShumpei Masuda, Tsuyoshi Yamamoto, Shuji Nakamura et al. · 2026 · cited 1 time · Not summarized yet
Engineered two-photon dissipative confinement uses a SISIS quantum circuit refrigerator to remove Kerr-cat excitations, rather than resonant transfer to a lossy readout mode.
Abstract
Kerr-cat qubits realized in periodically driven superconducting nonlinear resonators are a promising platform for quantum information processing with biased noise. Pure dephasing in such systems induces leakage out of the qubit subspace, motivating the use of quantum circuit refrigeration (QCR) to remove excess excitations. While conventional superconductor--insulator--normal-metal--insulator--superconductor (SINIS)-based QCRs can suppress leakage via single-photon absorption, they also enhance QCR-induced phase-flip errors. Here we investigate a QCR based on a superconductor--insulator--superconductor--insulator--superconductor (SISIS) junction coupled to a Kerr parametric oscillator (KPO).…
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Preserving Phase Coherence and Linearity in Cat Qubits with Exponential Bit-Flip SuppressionH. Putterman, K. Noh, Rishi N. Patel et al. · 2024 · Physical Review X · cited 27 times · Not summarized yet
Preserving Phase Coherence and Linearity in Cat Qubits with Exponential Bit-Flip Suppression addresses buffer-mode loss and nonlinearities in two-photon-dissipative cat qubits, not Kerr-cat excitation cooling.
Abstract
Cat qubits, a type of bosonic qubit encoded in a harmonic oscillator, can exhibit an exponential noise bias against bit-flip errors with increasing mean photon number. Here, we focus on cat qubits stabilized by two-photon dissipation, where pairs of photons are added and removed from a harmonic oscillator by an auxiliary, lossy buffer mode. This process requires a large loss rate and strong nonlinearities of the buffer mode that must not degrade the coherence and linearity of the oscillator. In this work, we show how to overcome this challenge by coloring the loss environment of the buffer mode with a multipole filter and optimizing the circuit to take into account additional inductances in …
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Autoparametric Resonance Extending the Bit-Flip Time of a Cat Qubit up to 0.3 sA. Marquet, Antoine Essig, Joachim Cohen et al. · 2023 · Physical Review X · cited 32 times · Not summarized yet
Autoparametric Resonance Extending the Bit-Flip Time of a Cat Qubit up to 0.3 s also uses engineered dissipation to extend cat-qubit bit-flip protection.
Abstract
Cat qubits, for which logical $|0\rangle$ and $|1\rangle$ are coherent states $|\pm\alpha\rangle$ of a harmonic mode, offer a promising route towards quantum error correction. Using dissipation to our advantage so that photon pairs of the harmonic mode are exchanged with single photons of its environment, it is possible to stabilize the logical states and exponentially increase the bit-flip time of the cat qubit with the photon number $|\alpha|^2$. Large two-photon dissipation rate $\kappa_2$ ensures fast qubit manipulation and short error correction cycles, which are instrumental to correct the remaining phase-flip errors in a repetition code of cat qubits. Here we introduce and operate an …
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High-Coherence Kerr-Cat Qubit in 2D ArchitectureAhmed Hajr, B. Qing, Ke Wang et al. · 2024 · Physical Review X · cited 47 times · Not summarized yet
High-Coherence Kerr-Cat Qubit in 2D Architecture addresses coherence and bit-flip protection in Kerr-cat qubits, focusing on architecture and drive-induced heating.
Abstract
The Kerr-cat qubit is a bosonic qubit in which multiphoton Schrödinger cat states are stabilized by applying a two-photon drive to an oscillator with a Kerr nonlinearity. The suppressed bit-flip rate with increasing cat size makes this qubit a promising candidate to implement quantum error correction codes tailored for noise-biased qubits. However, achieving strong light-matter interactions necessary for stabilizing and controlling this qubit has traditionally required strong microwave drives that heat the qubit and degrade its performance. In contrast, increasing the coupling to the drive port removes the need for strong drives at the expense of large Purcell decay. By integrating an effect…
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Enhancing bosonic qubit protection by squeezingRémi Rousseau, Diego Ruiz, E. Albertinale et al. · 2025 · Nature Communications · cited 22 times · Not summarized yet
Enhancing bosonic qubit protection by squeezing extends cat-qubit bit-flip times by deforming the encoded states, rather than cooling Kerr-cat excitations.
Abstract
Dissipative cat-qubits are a promising architecture for quantum processors due to their built-in quantum error correction. By leveraging two-photon stabilization, they achieve an exponentially suppressed bit-flip error rate as the distance in phase-space between their basis states increases, incurring only a linear increase in phase-flip rate. This property substantially reduces the number of qubits required for fault-tolerant quantum computation. Here, we implement a squeezing deformation of the cat qubit basis states, further extending the bit-flip time while minimally affecting the phase-flip rate. We demonstrate a steep reduction in the bit-flip error rate with increasing mean photon num…
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Quantum control of a cat qubit with bit-flip times exceeding ten secondsUlysse R'eglade, A. Bocquet, Ronan Gautier et al. · 2023 · Nature · cited 121 times · Not summarized yet
Quantum control of a cat qubit with bit-flip times exceeding ten seconds studies fast control while maintaining long bit-flip protection in a cat qubit.
Abstract
Quantum bits (qubits) are prone to several types of error as the result of uncontrolled interactions with their environment. Common strategies to correct these errors are based on architectures of qubits involving daunting hardware overheads1. One possible solution is to build qubits that are inherently protected against certain types of error, so the overhead required to correct the remaining errors is greatly reduced2–7. However, this strategy relies on one condition: any quantum manipulations of the qubit must not break the protection that has been so carefully engineered5,8. A type of qubit known as a cat qubit is encoded in the manifold of metastable states of a quantum dynamical system…
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Combined Dissipative and Hamiltonian Confinement of Cat QubitsRonan Gautier, A. Sarlette, M. Mirrahimi · 2021 · PRX Quantum · cited 48 times · Not summarized yet
Combined Dissipative and Hamiltonian Confinement of Cat Qubits combines two confinement mechanisms, whereas this paper uses resonant dissipation to cool Kerr-cat excitations.
Abstract
Quantum error correction with biased-noise qubits can drastically reduce the hardware overhead for universal and fault-tolerant quantum computation. Cat qubits are a promising realization of biased-noise qubits as they feature an exponential error bias inherited from their non-local encoding in the phase space of a quantum harmonic oscillator. To confine the state of an oscillator to the cat qubit manifold, two main approaches have been considered so far: a Kerr-based Hamiltonian confinement with high gate performances, and a dissipative confinement with robust protection against a broad range of noise mechanisms. We introduce a new combined dissipative and Hamiltonian confinement scheme bas…
Prior work it builds on
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Engineering fast bias-preserving gates on stabilized cat qubitsQiang-Da Xu, J. Iverson, F. Brandão et al. · 2021 · Physical Review Research · cited 53 times · Not summarized yet
Engineering fast bias-preserving gates on stabilized cat qubits applies leakage-suppression techniques to fast Kerr-cat gates, rather than using them to cool excitations.
Abstract
Stabilized cat codes can provide a biased noise channel with a set of bias-preserving (BP) gates, which can significantly reduce the resource overhead for fault-tolerant quantum computing. All existing schemes of BP gates, however, require adiabatic quantum evolution, with performance limited by excitation loss and non-adiabatic errors during the adiabatic gates. In this work, we apply a derivative-based leakage suppression technique to overcome non-adiabatic errors, so that we can implement fast BP gates on Kerr-cat qubits with improved gate fidelity while maintaining high noise bias. When applied to concatenated quantum error correction, the fast BP gates can not only improve the logical e…
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Stabilization and operation of a Kerr-cat qubitA. Grimm, N. Frattini, S. Puri et al. · 2020 · Nature · cited 516 times · Not summarized yet
Stabilization and operation of a Kerr-cat qubit establishes the Kerr-cat platform that this paper uses to study autonomous excitation cooling.
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Stabilizing a Bosonic Qubit Using Colored Dissipation.H. Putterman, J. Iverson, Qiang-Da Xu et al. · 2021 · Physical Review Letters · cited 33 times · Not summarized yet
Stabilizing a Bosonic Qubit Using Colored Dissipation proposes frequency-selective dissipation to remove leakage from protected qubit manifolds, akin to this paper’s resonant cooling.
Abstract
Protected qubits such as the 0-π qubit, and bosonic qubits including cat qubits and Gottesman-Kitaev-Preskill (GKP) qubits offer advantages for fault tolerance. Some of these protected qubits (e.g., 0-π qubit and Kerr-cat qubit) are stabilized by Hamiltonians which have (near-)degenerate ground state manifolds with large energy gaps to the excited state manifolds. Without dissipative stabilization mechanisms the performance of such energy-gap-protected qubits can be limited by leakage to excited states. Here, we propose a scheme for dissipatively stabilizing an energy-gap-protected qubit using colored (i.e., frequency-selective) dissipation without inducing errors in the ground state manifol…
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Repetition Cat Qubits for Fault-Tolerant Quantum ComputationJérémie Guillaud, M. Mirrahimi · 2019 · Physical Review X · cited 251 times · Not summarized yet
Repetition Cat Qubits for Fault-Tolerant Quantum Computation develops error-correction protocols that exploit cat-qubit noise bias, the protection this paper strengthens.
Abstract
We present a 1D repetition code based on the so-called cat qubits as a viable approach toward hardware-efficient universal and fault-tolerant quantum computation. The cat qubits that are stabilized by a two-photon driven-dissipative process, exhibit a tunable noise bias where the effective bit-flip errors are exponentially suppressed with the average number of photons. We propose a realization of a set of gates on the cat qubits that preserve such a noise bias. Combining these base qubit operations, we build, at the level of the repetition cat qubit, a universal set of fully protected logical gates. This set includes single-qubit preparations and measurements, NOT, controlled-NOT, and contro…
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Two-photon driven Kerr quantum oscillator with multiple spectral degeneraciesD. Ruiz, Ronan Gautier, Jérémie Guillaud et al. · 2022 · Physical Review A · cited 31 times · Not summarized yet
Two-photon driven Kerr quantum oscillator with multiple spectral degeneracies studies how Kerr-oscillator parameters affect bit-flip suppression in a closely related qubit.
Abstract
Kerr nonlinear oscillators driven by a two-photon process are promising systems to encode quantum information and to ensure a hardware-efficient scaling towards fault-tolerant quantum computation. In this paper, we show that an extra control parameter, the detuning of the two-photon drive with respect to the oscillator resonance, plays a crucial role in the properties of the defined qubit. At specific values of this detuning, we benefit from strong symmetries in the system, leading to multiple degeneracies in the spectrum of the effective confinement Hamiltonian. Overall, these degeneracies lead to a stronger suppression of bit-flip errors. We also study the combination of such Hamiltonian c…
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Updated on 10 November 2026.